Reduction of second order distortion in real time

ABSTRACT

In a radio receiver, a method of reducing second order distortion components, involves at a first mixer, mixing an input signal with an oscillator signal to generate an I component of a received radio signal; at a second mixer, mixing the input signal with a phase shifted oscillator signal to generate a Q component of the received radio signal; where the I and Q components of the received signal have a receive bandwidth; computing an estimate of second order distortion components as a power output of the I and Q components between approximately the receive bandwidth and twice the receive bandwidth of the received radio signals; and adjusting an operational parameter of the radio receiver to reduce the estimated value of second order distortion components. This abstract is not to be considered limiting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. patent applications:application Ser. No. ______, Attorney Docket Number 36197-US-PAT;application Ser. No. ______, Attorney Docket Number 37420-US-PAT; andapplication Ser. No. ______, Attorney Docket Number 36311-US-PAT, eachfiled on even date herewith, which are incorporated herein in theirentireties.

BACKGROUND

In a two way transceiver (transmitter/receiver) device such as acellular telephone, signals from the transmitter can enter the receivercreating second order products that behave like noise to the receiver.This can undesirably degrade the signal-to-noise ratio of the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the present disclosure will be described belowwith reference to the included drawings such that like referencenumerals refer to like elements and in which:

FIG. 1 is an example frequency spectrum showing the effects of IIP2distortion.

FIG. 2 is an example block diagram of a portion of a transceiver device100 in accordance with aspects of the present disclosure.

FIG. 3 is an example flow chart block of a process consistent withcertain aspects of the present disclosure.

FIG. 4 is a block diagram of an example circuit arrangement in whichprocessor 50 adjusts a filter parameter.

FIG. 5 is a diagram of an example circuit arrangement in which processor50 adjusts a gate bias in one or more of the mixer circuits.

DETAILED DESCRIPTION

For simplicity and clarity of illustration, reference numerals may berepeated among the figures to indicate corresponding or analogouselements. Numerous details are set forth to provide an understanding ofthe embodiments described herein. The embodiments may be practicedwithout these details. In other instances, well-known methods,procedures, and components have not been described in detail to avoidobscuring the embodiments described. The invention is not to beconsidered as limited to the scope of the embodiments described herein.

The terms “a” or “an”, as used herein, are defined as one or more thanone. The term “plurality”, as used herein, is defined as two or morethan two. The term “another”, as used herein, is defined as at least asecond or more. The terms “including” and/or “having”, as used herein,are defined as comprising (i.e., open language). The term “coupled”, asused herein, is defined as connected, although not necessarily directly,and not necessarily mechanically. The term “program” or “computerprogram” or “application” or similar terms, as used herein, is definedas a sequence of instructions designed for execution on a computersystem. A “program”, or “computer program”, may include a subroutine, afunction, a procedure, an object method, an object implementation, in anexecutable application, an applet, a servlet, a source code, an objectcode, a shared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer system. The term“processor”, “controller”, “CPU”, “Computer” and the like as used hereinencompasses both hard programmed, special purpose, general purpose andprogrammable devices and may encompass a plurality of such devices or asingle device in either a distributed or centralized configurationwithout limitation.

Reference throughout this document to “one embodiment”, “certainembodiments”, “an embodiment”, “an example”, “an implementation”, “anexample” or similar terms means that a particular feature, structure, orcharacteristic described in connection with the embodiment, example orimplementation is included in at least one embodiment, example orimplementation of the present invention. Thus, the appearances of suchphrases or in various places throughout this specification are notnecessarily all referring to the same embodiment, example orimplementation. Furthermore, the particular features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments, examples or implementations without limitation.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination. Therefore, “A, B or C” means “any ofthe following: A; B; C; A and B; A and C; B and C; A, B and C”. Anexception to this definition will occur only when a combination ofelements, functions, steps or acts are in some way inherently mutuallyexclusive.

In radio systems such as the cellular 3G and 4G LTE radio systems orother wireless communication systems, a transceiver (e.g., a mobiledevice such as a cellular telephone) transmits power that can leak backinto the transceiver's own receiver (i.e. through the receiver path).This causes problems for the receiver since this power often fallsdirectly within the receiver frequency due to “2nd order” non-linearityproduction of second order distortion components (also referred to as“IIP2”). This can be especially problematic in modern radio receiverarchitectures.

Because of this second order distortion, the signal that thetransceiver's receiver receives is equal to the desired incoming signal(RX—what the device is supposed to receive) plus some proportion of thetransmit signal squared (ignoring noise and other factors). This can berepresented mathematically as:

Receiver input signal=RX+c*(TX)²,

where RX represents the desired signal to be received, and ‘c’ is aconstant of proportionality of the (TX)² signal. Ideally, c=0 and thereceiver only receives signal RX. The signal due to (TX)² is effectivelyjust noise that corrupts the signal RX that the receiver is trying toreceive. Moreover, this signal has a bandwidth that is twice the normalRX bandwidth B. Hence, in accord with the present teachings, a measureof the signal present just outside the RX bandwidth B up to about 2B infrequency can be used to determine how much of the IIP2 signal ispresent, and steps can be taken to decrease the second order distortion.

Note that the signal RX may be considered complex, i.e., can be writtenas I+jQ, where j=√{square root over (−1)}, that is, “I” is the realpart, and “Q” is the imaginary part.

The second order distortion/interference signals IIP2 can be measuredwithout the presence of the desired receive signal in the factory orduring power up of the transceiver (e.g., telephone). However, thismethod does not allow one to correct the operation of the radio in realtime as it is working within a wireless network. Since various factorssuch as age, temperature, component drift, surroundings, etc. can causevariations in the amount of IIP2 distortion signals that are introducedin the receive path, initial factory settings may not be optimal.

In order to be able to more fully address the problem of second orderinterference, in accord with the present teachings the transceiver canexamine the received signal in real time while the transceiver isactually receiving the RX signal. By doing this the amount of 2nd ordersignal can be estimated by estimating the power in the band between Band 2B. Once the second order signal is estimated, adjustments can bemade to state variables that affect the operational parameters of thereceiver (e.g., filter bandwidth, filter Q, mixer bias levels, etc.) toreduce the 2nd order distortion signal components, e.g., using aniterative process.

Therefore, in accordance with certain aspects of the present disclosure,in a radio receiver, a method of reducing second order distortioncomponents, involves at a first mixer, mixing an input signal with anoscillator signal to generate an I component of a received radio signal;at a second mixer, mixing the input signal with a phase shiftedoscillator signal to generate a Q component of the received radiosignal; where the I and Q components of the received signal have areceive bandwidth; computing an estimate of second order distortion as apower output of the I and Q components between approximately the receivebandwidth and twice the receive bandwidth of the received radio signals;and adjusting an operational parameter of the radio receiver to reducethe estimated value of second order distortion components.

In certain implementations, the operational parameter of the radioreceiver comprises an operational parameter of one or both of the firstand second mixers. In certain implementations, the operational parameterof the radio receiver comprises bias levels of one or both of the firstand second mixers. In certain implementations, the bias level comprisesa gate bias voltage of one or both of the first and second mixers. Incertain implementations, the bias level comprises a bulk bias voltage ofone or both of the first and second mixers. In certain implementations,the operational parameter of the radio receiver comprises an operationalparameter of a filter. In certain implementations, the operationalparameter of the filter comprises a filter Q or bandwidth. In certainimplementations, the operational parameter of the filter comprises anotch frequency.

A radio receiver consistent with certain implementations has a localoscillator and a first mixer, configured to mix an input signal with alocal oscillator signal from the local oscillator to generate an Icomponent of a received radio signal. A second mixer is configured tomix the input signal with a phase shifted local oscillator signal togenerate a Q component of the received radio signal. The I and Qcomponents of the received signal have a receive bandwidth. A processoris programmed to: compute an estimate of second order distortion as apower of the I and Q components between approximately the receivebandwidth and twice the receive bandwidth of the received radio signals;and adjust an operational parameter of the radio receiver to reduce theestimate of second order distortion components.

In certain implementations, the operational parameter of the radioreceiver comprises an operational parameter of one or both of the firstand second mixers. In certain implementations, the operational parameterof the radio receiver comprises bias levels of one or both of the firstand second mixers. In certain implementations, the bias level comprisesa gate bias voltage of one or both of the first and second mixers. Incertain implementations, the bias level comprises a bulk bias voltage ofone or both of the first and second mixers. In certain implementations,one or more digital to analog converters is coupled to the processor andconfigured to convert digital control signals from the processor to avoltage that sets a bias level of one or both of the first and secondmixers. In certain implementations, one or more digital to analogconverters is coupled to the processor and configured to convert digitalcontrol signals from the processor to a voltage that sets a gate bias ofone or both of the first and second mixers. In certain implementations,the operational parameter of the radio receiver comprises an operationalparameter of a filter. In certain implementations, the operationalparameter of the filter comprises a filter Q or bandwidth. In certainimplementations, the operational parameter of the filter comprises afilter notch frequency.

Another radio receiver has a local oscillator and a first mixer,configured to mix an input signal with a local oscillator signal fromthe local oscillator to generate an I component of a received radiosignal. A second mixer is configured to mix the input signal with aphase shifted local oscillator signal to generate a Q component of thereceived radio signal. The I and Q components of the received signalhave a receive bandwidth. A programmed processor is provided. One ormore digital to analog converters is coupled to the processor andconfigured to convert digital control signals from the processor avoltage that sets a bias level of one or both of the first and secondmixers. The processor is programmed to: compute an estimate of secondorder distortion as a power output of the I and Q components betweenapproximately the receive bandwidth and twice the receive bandwidth ofthe received radio signals; and adjust an operational parameter of theradio receiver to reduce the estimate of second order distortioncomponents. In certain implementations, the bias level comprises a gateor bulk bias.

Referring to FIG. 1, an abstract graph of power output spectrum of areceiver's mixers is depicted in the presence of IIP2 distortion. Inthis graph, the desired RX signal's spectrum goes out to the receivebandwidth of B and is shown as 6. The spectrum of the IIP2, however,goes from zero to about 2B. In accord with examples consistent with thepresent teachings, one can deduce how a particular set of statevariables will affect the IIP2 performance of the receiver by measuringthe effect of varying the state variables while monitoring the spectrumin the range of B through 2B. This may be done at particular ranges offrequencies therein, or by measuring power in the entire band B to 2B,for example by a processor using a fast Fourier transform (FFT) analysisof the IQ signals. Those skilled in the art will appreciate that the RXbandwidth B is idealized in this figure, but is generally a designparameter for the bandwidth B that will contain the significant energyin RX band that can normally be used to decode the RX signal. Somedeviation from this ideal bandwidth is to be expected with real signalsand filters.

With reference to FIG. 2, in certain embodiments, a method is providedfor measuring and tuning the IIP2 of a radio receiver using real timecommunication signals. In the embodiment discussed herein, the radioreceiver has a pair of mixers 10 and 14 that produce outputs by mixingtheir input signal 18 with local oscillator signals 22 and 26 (which are90 degrees out of phase) in order to produce quadrature I and Q outputsignals 30 and 34 coming from the pair of mixers. These I and Q outputsignals 30 and 34 respectively are mixed by mixers 10 and 14 down tobaseband in a single conversion and are the signals that are decodedafter filtering at low pass filters 38 and 42. While this discussionpresumes a single conversion radio receiver, the present techniques areequally applicable to multiple conversion receivers.

In accord with certain implementations, the mixers 10 and 14 may havecontrollable parameters that can be adjusted directly or indirectly by aprocessor 50. Such controllable parameters can have an effect on theamount of 2nd order distortion produced at the output of the mixers andhence at the output of the filters. Processor 50 operates based oninstructions stored in a memory 54 that includes instructions 58 thatestimate the second order distortion and control the transceiver in amanner that helps to minimize such second order distortion components.Hence, a method can be provided to estimate/measure the second orderdistortion signal in the presence of a wanted signal during operation ofthe transceiver in the field. By taking this measurement, the secondorder terms can be minimized using a closed loop approach.

In the example transceiver of FIG. 2, the I signal 30 and the Q signal34 are processed in the radio transceiver in order to carry outreception of a transmitted communication. Interference is superimposedon these signals, and in the current example, second order componentsare one type of interference signal that can be superimposed on thewanted signal thus reducing the SNR (signal to noise ratio). It shouldbe noted that second order distortion can be very significant in today'stransceivers that use an architecture called “direct conversion”,“single conversion” or “zero-IF”. If the second order interference islabelled as ‘TX’, the desired ‘RX’ signal has I and Q signal componentsat 30 and 34 that become:

I->I+a(TX)²

Q->Q+b(TX)²

where a and b are coefficients that indicate the amount of second orderdistortion (for purposes of this analysis, the second order distortionis primarily in the form of power resulting from receipt of transmittedsignal TX from the transmitter portion of the transceiver and otherforms of noise and interference are presumed negligible). If there is nosecond order distortion, a=0 and b=0.

Therefore the average power of the I and Q signals become:

Average Power I-><I ² >+a<TX ²>

Average Power Q-><Q ² >+b<TX ²>

where the symbols < > denote averages over time.

By knowing that a large portion of this power TX² appears in thebandwidth between B and 2B this information can be used in a closed loopsystem that minimizes the power between B and 2B to estimate the secondorder distortion. Hence, referring back to FIG. 2, instructions 58 areused by processor 50 to sample the power in the I and Q signals(converted to the digital domain and fed back to processor 50) between Band 2B (e.g., by use of FFT analysis or other suitable method) andcompute an estimate of the second order distortion power in that band.The processor 50 can then increment a suitable transceiver parameter tosee how the incrementing of the transceiver parameter affects the secondorder distortion. The process can then be iterated so as to minimize thesecond order distortion. In one example, a parameter of the mixers 10and 14, such as the mixer gate bias or bulk (substrate), can be adjustedand the measurement and estimation of the second order distortion aspower between B and 2B repeated to determine if it has improved ordegraded. This process can be repeated until, for example, an optimum oracceptable amount of mixer bias is achieved for one or both mixers orany of the mixer components.

It is noted, however, that multiple effects may be caused by such anadjustment in an attempt to optimize IIP2 distortion. For example, ifthe mixer bias is changed, current drain can increase. So, if the IIP2distortion is within acceptable bounds, it may be unnecessary to fullyoptimize the mixer properties to achieve the absolute best IIP2distortion performance, provided that the IIP2 distortion performancecan be improved to be within acceptable limits. In all cases, what isoptimum may have to be determined by the process or using a suitablealgorithm which may optimize more than simply the IIP2 distortionperformance. In this example, once IIP2 performance is improved to anadequate degree, if current drain is increasing it may be advantageousto not fully optimize the IIP2 distortion in favour of having adequateIIP2 distortion performance and lower current drain (to maintain longbattery life).

It is noted that in FIG. 2, analog to digital and digital to analogconversions are omitted to simplify the figure, but those skilled in theart will understand that the I and Q signals are converted to digitalfor processing by processor 50 and the control signals that modify atransceiver parameter may be analog or digital, and hence, may beconverted to analog when appropriate.

Hence, in accord with an implementation of the above discussion, thesignal in the band between B and 2B is measured as an indicator of theamount of IIP2 signal present. This power is minimized or reduced by themixer input(s) that control the amount of 2nd order distortion produced.

One example process for carrying out the optimization of the secondorder distortion components is depicted as process 100 of FIG. 3starting at 104 after a decision is made to optimize the IIP2performance of the transceiver. Such a decision can be based upon anynumber of criteria, such as for example: passage of a specified timeperiod, change in SNR, observed degradation of radio performanceaccording to any specified criterion, power up of the radio, receipt ofa signal of a designated type, etc.

Once the process 100 is initiated at 104, input signals are received atthe receiver's mixers at 108 and converted to I and Q components bymixing with local oscillator signals that are separated in phase by 90degrees at 112. The I and Q values are then sampled by the processor 50to compute an estimate of the second order distortion components at 120,for example over a period of, for example, approximately tenmicroseconds. Thus at 124, the process can be iterated to adjust areceiver parameter such as the mixer bias to minimize or reduce thepower between B and 2B.

In this manner, the IIP2 components can be minimized or alternativelyreduced to an acceptable level while optimizing other receiverperformance parameters. When the optimization is in progress themeasuring and adjusting as described above are iterated until theprocessor 50 deems the system optimized or adequately adjusted. This isdepicted as a “no” decision at 130 at which point control returns to104. At the point where the processor 50 deems the system to be suitablyoptimized in terms of IIP2 alone or in conjunction with one or moreother performance parameters, control passes to block 136 and theprocess ends until invoked again.

Referring now to FIG. 4, in certain implementations processor 50 can beconfigured to receive the I and Q signals as depicted in FIG. 2 andprovide an output control signal to one or more digital to analogconverters (DAC) 202 to control an operational parameter of a filtersuch as filter 206 (which may be before or after a low noise amplifier).Of course, this example presumes a filter 206 that is adjusted withanalog signals. For control using digital signals, the DAC 202 is notused. In this example, the filter parameters being controlled relate toan output from a low noise amplifier 210 coupled to an antenna toreceive the RX input signal. Filter 206 can be configured as a low passfilter, a band pass filter or a notch filter in any other suitablefilter configuration. The control exercised by processor 50 can be tocontrol the bandwidth, center frequency, notch frequency, Q or otherfilter parameter as may be deemed in a particular radio configuration toimpact the second order distortion components that appear in thereceiver.

Referring now to FIG. 5, in certain implementations processor 50 can beconfigured to receive the I and Q signals as depicted in FIG. 2 andprovide an output control signal to one or more of the mixers 10 and 14,shown in greater detail in this illustration. In this example the mixersare configured to operate on differential signals and hence mixer 10receives signals LO− and LO+ from the local oscillator. Similarly, mixer14 receives differential signals LO− and LO+ from its local oscillatorsource (which may be the same local oscillator with multiple phaseoutputs) with the mixer 10 receiving local oscillator signals that are90 degrees out of phase with those received by mixer 14. Each localoscillator signal is shown capacitively coupled to the respective gatesof transistors 220, 222 of mixer 10, and 224, 226 of mixer 14.

Processor 50 sends control signals to DACs 230, 232, 234 and 236 tocontrol an operational parameter the mixer transistors 220, 222, 224 and226 respectively. In this example, the gate bias is controlled by theoutput of DACs 230, 232, 234 and 236 through resistors 240, 242, 244 and246 respectively by changing the analog voltage applied to therespective resistors. The sources of transistors 220, 222, 224 and 226are coupled to differential supply voltages VBB− and VBB+ while thedrains of transistors 220, 222 are coupled together and receive the RFinput voltage in a differential manner so that VRF+ is received by mixer10 and VRF− is received at the drains of transistors 224 and 226 whichare also coupled together.

In this example, the bias of each of the transistor pair making up mixer10 and the transistor pair making up mixer 14 can be individuallycontrolled to optimize the operation of the mixer and reduce or minimizethe second order distortion components as previously described. One ormore gate bias can be adjusted to achieve the desired change inoperation of the mixers. In other implementations, other parameters ofthe mixers could be adjusted such as the signal level from theoscillator, bulk or substrate bias, or the RF input level to thereceiver. Other variations will occur to those skilled in the art uponconsideration of the present teachings.

The order in which the optional operations represented in process 100occur is not predetermined or predefined, and these operations may occurin any operational order. Thus, while the blocks comprising the methodsare shown as occurring in a particular order, it will be appreciated bythose skilled in the art that many of the blocks are interchangeable andcan occur in different orders than that shown without materiallyaffecting the end results of the methods.

The implementations of the present disclosure described above areintended to be examples only. Those of skill in the art can effectalterations, modifications and variations to the particular exampleembodiments herein without departing from the intended scope of thepresent disclosure. Moreover, selected features from one or more of theabove-described example embodiments can be combined to createalternative example embodiments not explicitly described herein.

It will be appreciated that any module or component disclosed hereinthat executes instructions may include or otherwise have access tonon-transitory and tangible computer readable media such as storagemedia, computer storage media, or data storage devices (removable ornon-removable) such as, for example, magnetic disks, optical disks, ortape data storage, where the term “non-transitory” is intended only toexclude propagating waves and signals and does not exclude volatilememory or memory that can be rewritten. Computer storage media mayinclude volatile and non-volatile, removable and non-removable mediaimplemented in any method or technology for storage of information, suchas computer readable instructions, data structures, program modules, orother data. Examples of computer storage media include RAM, ROM, EEPROM,flash memory or other memory technology, CD-ROM, digital versatile disks(DVD) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices, or any othermedium which can be used to store the desired information and which canbe accessed by an application, module, or both. Any such computerstorage media may be part of the server, any component of or related tothe network, backend, etc., or accessible or connectable thereto. Anyapplication or module herein described may be implemented using computerreadable/executable instructions that may be stored or otherwise held bysuch computer readable media.

The present disclosure may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the disclosure is, therefore,indicated by the appended claims rather than by the foregoingdescription. All changes that come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. In a radio receiver, a method of reducing secondorder distortion components, comprising: at a first mixer, mixing aninput signal with an oscillator signal to generate an I component of areceived radio signal; at a second mixer, mixing the input signal with aphase shifted oscillator signal to generate a Q component of thereceived radio signal; where the I and Q components of the receivedsignal have a receive bandwidth; computing an estimate of second orderdistortion components as a power output of the I and Q componentsbetween approximately the receive bandwidth and twice the receivebandwidth of the received radio signals; and adjusting an operationalparameter of the radio receiver to reduce the estimated value of secondorder distortion components.
 2. The method in accordance with claim 1,where the operational parameter of the radio receiver comprises anoperational parameter of one or both of the first and second mixers. 3.The method in accordance with claim 1, where the operational parameterof the radio receiver comprises bias levels of one or both of the firstand second mixers.
 4. The method in accordance with claim 3, where thebias level comprises a gate bias voltage of one or both of the first andsecond mixers.
 5. The method in accordance with claim 3, where the biaslevel comprises a bulk bias voltage of one or both of the first andsecond mixers.
 6. The method in accordance with claim 1, where theoperational parameter of the radio receiver comprises an operationalparameter of a filter.
 7. The method in accordance with claim 6, wherethe operational parameter of the filter comprises a filter Q orbandwidth.
 8. The method in accordance with claim 6, where theoperational parameter of the filter comprises a notch frequency.
 9. Aradio receiver, comprising: a local oscillator; a first mixer,configured to mix an input signal with a local oscillator signal fromthe local oscillator to generate an I component of a received radiosignal; a second mixer, configured to mix the input signal with a phaseshifted local oscillator signal to generate a Q component of thereceived radio signal; where the I and Q components of the receivedsignal have a receive bandwidth; a processor programmed to: compute anestimate of second order distortion components as a power of the I and Qcomponents between approximately the receive bandwidth and twice thereceive bandwidth of the received radio signals; and adjust anoperational parameter of the radio receiver to reduce the estimate ofsecond order distortion components.
 10. The radio receiver in accordancewith claim 9, where the operational parameter of the radio receivercomprises an operational parameter of one or both of the first andsecond mixers.
 11. The radio receiver in accordance with claim 9, wherethe operational parameter of the radio receiver comprises bias levels ofone or both of the first and second mixers.
 12. The radio receiver inaccordance with claim 11, where the bias level comprises a gate biasvoltage of one or both of the first and second mixers.
 13. The radioreceiver in accordance with claim 11, where the bias level comprises abulk bias voltage of one or both of the first and second mixers.
 14. Theradio receiver in accordance with claim 11, further comprising one ormore digital to analog converters coupled to the processor andconfigured to convert digital control signals from the processor to avoltage that sets a bias level of one or both of the first and secondmixers.
 15. The radio receiver in accordance with claim 11, furthercomprising one or more digital to analog converters coupled to theprocessor and configured to convert digital control signals from theprocessor to a voltage that sets a gate or a bulk bias of one or both ofthe first and second mixers.
 16. The radio receiver in accordance withclaim 9, where the operational parameter of the radio receiver comprisesan operational parameter of a filter.
 17. The radio receiver inaccordance with claim 16, where the operational parameter of the filtercomprises a filter Q or bandwidth.
 18. The radio receiver in accordancewith claim 16, where the operational parameter of the filter comprises afilter notch frequency.
 19. A radio receiver, comprising: a localoscillator; a first mixer, configured to mix an input signal with alocal oscillator signal from the local oscillator to generate an Icomponent of a received radio signal; a second mixer, configured to mixthe input signal with a phase shifted local oscillator signal togenerate a Q component of the received radio signal; where the I and Qcomponents of the received signal have a receive bandwidth; a programmedprocessor; one or more digital to analog converters coupled to theprocessor and configured to convert digital control signals from theprocessor to a voltage that sets a bias level of one or both of thefirst and second mixers; where the processor is programmed to: computean estimate of second order distortion components as a power output ofthe I and Q components between approximately the receive bandwidth andtwice the receive bandwidth of the received radio signals; and adjust anoperational parameter of the radio receiver to reduce the estimate ofsecond order distortion components.
 20. The radio receiver in accordancewith claim 19, where the bias level comprises a gate or bulk bias.